[SRU][Bionic][PATCH 1/1] KVM: PPC: Book3S HV: Fix guest r11 corruption with POWER9 TM workarounds

Joseph Salisbury joseph.salisbury at canonical.com
Thu Oct 11 20:06:12 UTC 2018

From: Michael Neuling <mikey at neuling.org>

BugLink: https://bugs.launchpad.net/bugs/1792501

When we come into the softpatch handler (0x1500), we use r11 to store
the HSRR0 for later use by the denorm handler.

We also use the softpatch handler for the TM workarounds for
POWER9. Unfortunately, in kvmppc_interrupt_hv we later store r11 out
to the vcpu assuming it's still what we got from userspace.

This causes r11 to be corrupted in the VCPU and hence when we restore
the guest, we get a corrupted r11. We've seen this when running TM
tests inside guests on P9.

This fixes the problem by only touching r11 in the denorm case.

Fixes: 4bb3c7a020 ("KVM: PPC: Book3S HV: Work around transactional memory bugs in POWER9")
Cc: <stable at vger.kernel.org> # 4.17+
Test-by: Suraj Jitindar Singh <sjitindarsingh at gmail.com>
Reviewed-by: Paul Mackerras <paulus at ozlabs.org>
Signed-off-by: Michael Neuling <mikey at neuling.org>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(cherry picked from commit f14040bca89258b8a1c71e2112e430462172ce93)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
 arch/powerpc/kernel/exceptions-64s.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 59f5cfa5449b..dcef07a22579 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1318,9 +1318,7 @@ EXC_REAL_BEGIN(denorm_exception_hv, 0x1500, 0x100)
 	mfspr	r10,SPRN_HSRR1
-	mfspr	r11,SPRN_HSRR0		/* save HSRR0 */
 	andis.	r10,r10,(HSRR1_DENORM)@h /* denorm? */
-	addi	r11,r11,-4		/* HSRR0 is next instruction */
 	bne+	denorm_assist
@@ -1386,6 +1384,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
+	mfspr	r11,SPRN_HSRR0
+	subi	r11,r11,4
 	mtspr	SPRN_HSRR0,r11
 	mtcrf	0x80,r9
 	ld	r9,PACA_EXGEN+EX_R9(r13)

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